When I was using the UFO/CO roaster I roasted strictly by weight, time, sound & color.
First, I like Full City or Full City Plus for espresso, and City Plus roast for all other methods of brewing coffee. For all roasts I found that 16 ozs of beans would get me to first crack in ~9 minutes at full power. After I had a rolling 1st I'd turn the roaster's dial back to 450?F and coast into second crack.
City Plus roast is about the best roast for drip and vac pot brewers. It brings out the varietal's flavor and is still dark enough to bring out some of the stronger base flavors. I judged this roast to be done by listening for the first outliers of 2nd, at which point I'd stop the heat and dump & cool the beans.
For Full City I'd ignore the outliers of 2nd and when it just started to sound busy, I'd stop the heat & dump the beans for cooling. For Full City Plus I'd again ignore the 2nd outliers and start timing as soon as 2nd got busy and let it go for 20 seconds, before stopping the roast.
Each roast has to be adjusted a bit because of variables that I don't fully understand. What I do know is that time is not absolute. Different beans take longer to get to 1st crack & 2nd crack. Some beans seem to all hit 1st & 2nd at about the same time, and then there are beans that never seem to have a definable start & finish to the different cracks.
Color seems to be the best indicator of roast levels. I've found that
Sweet Maria's pictorial guide works best for me. I use a white light LED lamp when I'm roasting in order to have consistent lighting from roast to roast. By comparing what I see in the pan to what I see on the guide I've been able to hit the roast I want pretty consistently.
So I'd say the UFO/CO roaster has been a good roaster for me. I've built them for friends and neighbors and helped online friends put theirs together. I've always told people interested in getting into the hobby to start with a homebuilt roaster rather than buying one. The money saved can be significant and I truly don't believe the ones you can buy perform any better than the UFO/CO or TurboCrazy roasters built for $100 or so.
That's my story & I'm sticking to it!